The Center for Biological Diversity on Wednesday, October 8, 2014 filed an emergency petition to protect the tricolored blackbird as endangered under the California Endangered Species Act. The Center cited the numerous threats faced by tricolored blackbirds and the dramatic decline documented most recently in this year's Statewide Survey. The Center's petition listed losses of native habitats, including wetlands, grasslands and shrublands, to agriculture, urbanization, market hunting and shooting in autumn when tricolors forage in mixed flocks on ripening rice with red-winged blackbirds, pesticide use, and harvest of grain fields while eggs and young are in the nests as among the factors resulting in the decline. The losses of native habitats and widespread pesticide use are the most likely causes of the chronic low productivity of the species, and the continuing severe drought is likely further stressing the species.
The 2014 Statewide Survey Final Report was released on July 31, 2014.
This report contains the results of the 2014 Statewide Survey, comparisons to past statewide surveys, and conservation recommendations.
The 2014 Statewide Survey was held from April 18-20, 2014. It appears to have been the most comprehensive Statewide Survey ever, with 143 participants surveying for tricolors at 802 locations in 41 counties.
The California population estimate derived from the Survey was 145,000 birds. This is a 44% reduction from the 258,000 birds seen during the 2011 Survey and a 63% reduction from the 395,000 birds seen during the 2008 Survey. Thus, the number of tricolors in California continues a rapid decline.
The number of birds declined most markedly in the San Joaquin Valley, where there were 78% fewer birds seen in 2014 than in 2008 (73,482 vs. 340,703), and along the Central Coast, where there were 91% fewer birds seen in 2014 than in 2008 (627 vs. 7014). The number of birds in the Sierra Nevada foothills was up 145% compared to 2008 (54,151 vs. 22,586), and the number of birds seen in southern California was up 126% compared to 2008 (12,386 vs. 5,487).
The recent sharp decline in the number of tricolors was highlighted on national television on Saturday, June 28th, 2014 on CBS Evening News. The story, by CBS News reporter Bigad Shaban, was recorded on Thursday, June 26th at the Conaway Ranch in Yolo County. The piece features research by U.C. Davis avian ecologist Dr. Bob Meese and cites the link between widespread and chronic reproductive failures to insufficient insects in the diets of breeding birds.
An article in the Fresno Bee highlights the plight of the tricolored blackbird and efforts being made to conserve at-risk colonies in silage grain fields and the recent, on-going severe population decline. It also mentions the 2014 Statewide Survey as an attempt to get a current population estimate.
The U.S. Fish and Wildlife Service has asked Dr. Bob Meese to coordinate the 2014 Tricolored Blackbird Statewide Survey. Monica Iglecia of Audubon California is assisting with Survey coordination.
The Statewide Survey will be conducted over three days - April 18th through the 20th, 2014.
The Statewide Survey relies upon county coordinators as well as volunteer participants to help to survey both historical colony locations as well as to survey in appropriate regions for new, previously undocumented colony locations and to estimate the number of birds at occupied sites. No prior experience is necessary to participate in the survey and any level of commitment, big or small, is welcome to help to make this year's survey as complete as possible.
Owens Creek, a tricolored blackbird breeding location in eastern Merced County, at the NW corner of Cunningham Road and Childs Avenue, was converted to an orchard in autumn, 2013, likely permanently eliminating this as a breeding location. Local landowners had informed U.C. Davis ecologist Dr. Bob Meese that upwards of 50,000 birds or more had been breeding there consistently since at least the 1960's and breeding had continued until 2011, when the landowners changed the management to conditions unfavorable to tricolor breeding. Tricolors had within the past decade been breeding in Merced County in increasing numbers, so the loss of this important site, which is surrounded by open pasture and has a dairy nearby and a creek running through it, is a setback for conservation efforts and reduces the number of breeding locations that are surrounded by productive foraging habitats.
This publication by U.C. Davis ecologist Bob Meese, which appeared in the journal Western Birds in summer, 2013, summarizes the results of 6 years of field work designed to evaluate the role of insect abundance on tricolored blackbird reproductive success.
A total of 47 colonies was studied and relative insect abundance and reproductive success at each was estimated. In only rare instances was reproductive success estimated to be 1 young/nest or greater, and in each case higher reproductive success was correlated with unusually high insect abundance in foraging habitats surrounding colonies.
Tricolor reproduction appears to be food-limited and few locations in the Central Valley appear to have the abundance of insects necessary to support reproduction by a colonial insectivorous bird species.
The most recent statewide surveys documented a rapid decline in the number of Tricolored Blackbirds, from about 400,000 in 2008 to about 250,000 3 years later. Annual monitoring and research into the relationship between reproductive success (RS) and insect abundance has shown a chronic low RS in dozens of colonies studied since 2007 and relatively high RS only in instances when colonies were surrounded by landscapes with unusually high insect abundance. Thus, the recent decline in the numbers of tricolors is believed to be due to chronic low RS (the number of birds recruiting into the population has been much smaller than the number dying) due to insufficient insect abundance. The decline in abundance is seen in the sizes of the largest colonies (Figure 1) from 2005 – 2013, where as recently as 2006 the average of the 5 largest colonies was nearly 72,000 birds, but in 2013 was less than 12,000 birds. And this decline in the sizes of the largest colonies comes at a time when researchers have documented a large number of colonies in new locations (Figure 2), nearly 100 since 2005. All else being equal, such a rapid increase in the number of known colony locations should have resulted in an increase in the population estimate, so the rapid decline in abundance is even more alarming. The next statewide survey, scheduled for April, 2014, will help to quantify the rate of decrease in the numbers of tricolors and provide a current statewide population estimate.